The next generation of passenger car motor oil and heavy duty diesel engine oil categories will require equivalent antiwear properties but with lower levels of phosphorus and sulfur in the formulations in order to reduce contamination of more stringent pollution control devices. It is well known that sulfur and phosphorus containing additives impart antiwear properties to a finished oil, and also may poison or otherwise reduce the effectiveness of pollution control devices.
Zinc dialkyl dithiophosphates (“Zn DDPs”) have been used in lubricating oils for many years. Zn DDPs also have good antiwear properties and have been used to pass cam wear tests, such as the Seq IVA and TU3 Wear Test. Many patents address the manufacture and use of Zn DDPs including U.S. Pat. Nos. 4,904,401; 4,957,649; 6,114,288, all of which are incorporated herein by reference in their entirety.
Sulfur-containing antiwear are also well known and include dihydrocarbyl polysulfides; sulfurized olefins; sulfurized fatty acid esters of both natural and synthetic origins; trithiones; sulfurized thienyl derivatives; sulfurized terpenes; sulfurized polyenes; sulfurized Diels-Alder adducts, etc. Specific examples include sulfurized isobutylene, sulfurized diisobutylene, sulfurized triisobutylene, dicyclohexyl polysulfide, diphenyl polysulfide, dibenzyl polysulfide, dinonyl polysulfide, and mixtures of di-tert-butyl polysulfides such as mixtures of di-tert-butyl trisulfide, di-tert-butyl tetrasulfide and di-tert-butyl pentasulfide, among others. Of the foregoing, sulfurized olefins are used in many applications. Methods of preparing sulfurized olefins are described in U.S. Pat. Nos. 2,995,569; 3,673,090; 3,703,504; 3,703,505; 3,796,661; and 3,873,454. Also useful are the sulfurized olefin derivatives described in U.S. Pat. No. 4,654,156. Other sulfur-containing antiwear agents are described in U.S. Pat. Nos. 4,857,214, 5,242,613, and 6,096,691.
A need exists for a lubricating additive that provides excellent antiwear properties and is more compatible with pollution control devices used for automotive and diesel engines.